GCC vs. LLVM-GCC Benchmarks

[kernelOfTruth]

I wonder how long it takes until Gentoo migrates to clang... Faster compile speed should be crucial there.

I think most of the other Gentoo users agree that the speed (and correctness) of the final code counts more than the time it needs for compilation

for me it's a bonus if it compiles faster than gcc or {insert other preferred compiler}

if e.g. llvm-gcc was 4 times faster during compilation of code but the final code/compiled binary with gcc (without llvm) was 3 times faster during execution than llvm-gcc I'd prefer gcc over llvm-gcc any time

[smitty3268]

Errr, what on Earth does that have to do with anything? That's just like complaining Sun's Java compiler doesn't compile C. :P

Gentoo is hardly going to switch to a compiler that 95% of it's users can't use. That's all I meant. (95% because there are a lot of C++ packages most people use, even in GNOME).

[nanonyme]

lso, clang itself doesn't support tons of code (think the entire KDE desktop) that's not written in C. They'd almost certainly have to start out using the GCC front-end to get most things working.

Errr, what on Earth does that have to do with anything? That's just like complaining Sun's Java compiler doesn't compile C. :P

[smitty3268]

It's a long, long way away from being supported on Gentoo. They are actually quite conservative when it comes to changing compilers, which makes sense when you think about it. They have to support all that code being compiled by users with different flags, and switching to a new compiler means going through every single emerge script and fixing every possible combination. Not an easy task to do, even for a gcc upgrade.

Also, clang itself doesn't support tons of code (think the entire KDE desktop) that's not written in C. They'd almost certainly have to start out using the GCC front-end to get most things working.

And judging by the benchmarks here, there might be a revolt among those "elite" users who stick on 50 different optimization flags to their CFLAGS in an effort to get any extra performance possible. I think the majority of Gentoo users are quite comfortable with letting the compiler work in the background for half an hour while they surf the web. Cutting that time to 20 minutes in exchange for reducing performance might not make much sense to a lot of them.

[kraftman]

I wonder how long it takes until Gentoo migrates to clang... Faster compile speed should be crucial there.

Gentoo maybe, but not Linux kernel. At least not now and probably not in the near future (if ever):

http://lkml.org/lkml/2009/5/8/388

the most interesting response IMO:

http://lkml.org/lkml/2009/5/9/59

[ioannis]

Can you guys do a comparison of modern gcc and llvm with Visual Studio and Intel's compiler? It would be interesting to see where the open source compilers are against the proprietary

[nanonyme]

I wonder how long it takes until Gentoo migrates to clang... Faster compile speed should be crucial there.

[b15hop]

Do a test of GCC vs Intel compiler and/or any other compiler. Compile time speed, run time speed, code size ... hmm..

[hdante]

I think the description of llvm-gcc is incorrect. llvm-gcc back end is not a modified version of gcc, it's llvm. llvm-gcc front end is a modified version of gcc front end. Please confirm.

And the results were really insightful.

[tettamanti]

When building these tests, is there a way to also build and affect the C runtime library.

Hum, probably you can manage to override the system library with LD_PRELOAD (or LD_LIBRARY_PATH).

While I can appreciate that many of these tests have "hard stuff" in their code, the performance of an app is always so dependent on the performance of it's underlying runtime library (for things like memcpy, strcmp, etc.) that I think it's worth a look.

For critical paths (like memcpy, strcmp, ...) the library is probably picking up the most appropriate hand-coded ASM version of the function